NASA says private-sector spaceships will have to satisfy safety standards that the space shuttle can’t meet — and the companies building those spaceships say they'll rise to the challenge.

Friday's 25th anniversary of the Challenger shuttle explosion is focusing fresh attention on the issue of spaceflight safety, with good reason. The loss of the shuttle and its crew of seven, including educator-astronaut Christa McAuliffe, dramatically highlighted the risks associated with the world's most complex flying machine.

Those risks were brought home again with the catastrophic breakup of the shuttle Columbia in 2003. Once again, seven astronauts were lost, due to inherent problems with the space shuttle's design as well as lapses in NASA's "safety culture."

The Challenger and Columbia disasters led risk analysts to estimate that flying the space shuttle carried a roughly 1-in-100 chance that the crew and the spaceship would be lost during a given mission. In the wake of the Columbia tragedy, NASA and the White House decided to retire the shuttle fleet and move on to a simpler, safer launch system.

When NASA was working on plans for its own crew launch system to replace the shuttle and service the International Space Station, the agency set standards that lowered the chance of crew loss to 1-in-1,000.

"Neither the shuttle nor the Russian Soyuz could meet these standards," said John Logsdon, former director of the Space Policy Institute at George Washington University and a member of the NASA Advisory Council's Exploration Committee.

Over the past year, the White House and NASA decided to go with a different approach, with the space agency purchasing services from commercial spaceship ventures. NASA is paying out hundreds of millions of dollars for the development of cargo ships such as SpaceX's Dragon capsule, which passed its first flight test last month. If the spaceships work as advertised, commercial companies would be in line for billions of dollars worth of contracts.

NASA eventually hopes to use commercial craft to ferry astronauts back and forth to the space station as well. But the job won't be easy. In a set of draft requirements issued last month, NASA said it expected commercial companies to measure up to the same risk standards the space agency expected for itself: a 1-in-1,000 chance that the crew would be lost during a journey to and from the space station.

"These are quite demanding and rigorous standards," Logsdon said.

Some space veterans think the commercial companies can't do it. Apollo 17 commander Gene Cernan — who was the last man to walk on the moon back in 1972 — complained to Congress last year that the new players in spaceflight "do not yet know what they don't know, and that can lead to dangerous and costly consequences."

Logsdon thinks the companies can do it. "I see no reason why a privately developed craft with NASA involved in a public-private partnership, perhaps to a greater degree than NASA has been involved with SpaceX to date, can't develop a spacecraft that meets these criteria," he said.

SpaceX thinks it can, too. The California-based company's millionaire founder, Elon Musk, has said repeatedly that he could have a crew-capable spaceship ready for use three years after getting NASA's go-ahead for the project.

But what about the 1-in-1,000 risk?

"It's difficult to put a physical measure to that number," said Ken Bowersox, a former NASA astronaut who is now SpaceX's vice president of astronaut safety, "but the idea is to have a vehicle that's safer than what's flying now."

Bowersox noted that the specific requirements for crew-capable vehicles were still under negotiation. Then he went on to say that, based on what NASA has put out so far, SpaceX has "a great chance of meeting those requirements."

The Boeing Co., which is the prime contractor for the International Space Station, strikes a similar tone. Boeing has proposed building a crew capsule called the CST-100 to send astronauts as well as paying passengers to the space station or other destinations.

"We will meet those requirements that NASA sets forth," said Edmund Memi, a spokesman for Boeing Space Exploration.

So what's the catch? First, there's cost. Bowersox said the development of a crew-capable Dragon would be "difficult to price right off the bat." One option would be to go with the traditional cost-plus arrangement used for building spacecraft — an arrangement that has led to escalating government expenses for programs in the past.

SpaceX would prefer to go with the type of fixed-price arrangement that was put into effect for the development of the Dragon cargo capsule and Falcon 9 rocket. But if that approach is used for developing a crew-capable Dragon, it would probably have to be done in well-defined phases, Bowersox said.

Bowersox's boss, Elon Musk, has said that the total development cost for a Dragon crew capsule would be on the order of $1 billion over three years. "To put that figure into perspective, that's roughly how much NASA will spend on Soyuz seats over the same period of time (assume six seats per year at an average of $55 million per seat)," Musk said in an e-mailed statement.

In addition to the dollars-and-cents issue, the commercial companies are wary of being too hamstrung by hundreds of pages of written requirements. Former space shuttle program director Wayne Hale, who retired from NASA last year, warned that excessive red tape could lead to a "train wreck" for the space agency's commercialization effort.

"The thing with commercial crew is, you've got to have some leeway to meet those requirements, as long as you meet them," Boeing's Memi said.

Logsdon said NASA could find itself on the horns of a political dilemma: If it sticks to its requirement-laden traditions, commercial space companies might well be heading for the train wreck that Hale is worried about. But if the agency is perceived as relaxing its requirements, it could face congressional criticism for going soft on safety.

"Backing off from the current NASA standards to something that could be more reasonable is going to be tricky," Logsdon said.

New and improved spaceflight?The commercialization effort is already leading to new, potentially improved approaches to spaceflight safety. For example, virtually every company working on a concept for a crew-capable spaceship is focusing on an innovative type of launch abort system that would push the capsule away from an out-of-control rocket.

The space shuttle has no launch escape system. If it did, there might have been a chance of saving Challenger's crew.

For its own future spacecraft, NASA had been focusing on the kind of launch escape tower system that was used during the Mercury and Apollo programs — but the "pusher" rocket system is more easily integrated into the capsule and won't go to waste after a successful launch. It can be used to control the spacecraft during its flight and descent, and reused on the missions that follow.

There are drawbacks: Tower systems have more "natural stability," SpaceX's Bowersox said, while pusher systems would require a more sophisticated control system. Also, a pusher abort system on a reusable spacecraft would have to be positioned to minimize the risk of damage during re-entry. Despite those drawbacks, SpaceX and other companies (such as Boeing, Sierra Nevada, Orbital Sciences and Blue Origin) are hard at work designing pushers with NASA funding.

"We think there are enough advantages to give that a try," Bowersox said.

Remembering past tragediesBowersox is well aware of what's at stake when it comes to spaceflight safety. When Columbia was lost in 2003, he was serving in orbit as commander of the International Space Station. He had to change his travel plans to come home on a Russian Soyuz craft rather than a space shuttle. And he still feels an ache over the loss of his friends in the astronaut corps.

"The emotions that come with that loss sometimes cause us to question what we do — and that questioning is healthy," he said.

So what kind of answer does Bowersox come up with? "This might sound corny," he said, "but I believe what we're doing now is critical for the future of our species. ... History will consider this a critical period in our existence, and I want to be part of that."

Ten thousand years from now, historians might well look at the present push into outer space as a turning point on a par with humanity's migrations out of Africa, or over the Bering Sea's land bridge into America, Bowersox said.

"The fact that space is a risky business, and that we have lost members of the astronaut profession, is one of the things that drive me at SpaceX," he said. "It is why I want to work on the safest, most reliable and economical vehicle for spaceflight."

With Challenger and Columbia in mind, would he ride that vehicle back into space? "The crew-transport Dragon that we're going to build will meet my standards, and I would feel confident riding on it," Bowersox said. "I'd love to fly on it, but I'm not assigned to a flight."